EXTRACT_SUBREG coalescing support. The coalescer now treats EXTRACT_SUBREG like

(almost) a register copy. However, it always coalesced to the register of the
RHS (the super-register). All uses of the result of a EXTRACT_SUBREG are sub-
register uses which adds subtle complications to load folding, spiller rewrite,
etc.

llvm-svn: 42899

1 files changed, 0 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
index b616b7e4825..bb5379c3491 100644
--- a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp
@@ -567,9 +567,6 @@ void ScheduleDAG::EmitSubregNode(SDNode *Node,
     // TODO: If the node is a use of a CopyFromReg from a physical register
     // fold the extract into the copy now
 
-    // TODO: Add tracking info to SSARegMap of which vregs are subregs
-    // to allow coalescing in the allocator
-    
     // Create the extract_subreg machine instruction.
     MachineInstr *MI =
       new MachineInstr(BB, TII->get(TargetInstrInfo::EXTRACT_SUBREG));